Abstract: A method for the estimation of pore pressure within a subterranean formation containing fluid during the drilling of a bore hole. The bore hole is drilled using a drill string consisting of a drill bit fitted to its lower end, and using drilling mud pumped from the surface through the drill string and finally evacuated.

Abstract: The method comprises during a drilling operation wherein the drilling fluid is set moving and the drill string is stationary, monitoring the pressure of the drilling fluid pumped into the drill string depending on the volume of liquid pumped in the drill string and determining, from the pressure curve, a physical property linked to the thixotropy of the drilling fluid. An advantage of the invention is that the highest point of the pressure curve indicating the start of the fluid flow into the well is easily visible, and its maximum value can be measured to find the gel strength specific value.

Abstract: In a method of assessing drilling conditions during a drilling operation measurements of torque applied (TOR), weight on bit (WOB), rate of penetration (ROP), and rotation speed (ROT) are gathered. Computed therefrom is a history (60, 61) of points (x, y) where x=(TOR/WOB) and y=(ROP/ROT).sup..gamma. : .gamma. being a derived constant indicative of down hole geometry. Trends in this history are monitored to assess drilling conditions. For example in soft plastic rock migration 62 towards the origin and in hard plastic rock migration 63 towards the abscissa is indicative of drill bit wear.

Abstract: A method for measuring the wear of milled tooth bits during oilwell drilling uses surface and subsurface wellsite sensors to determine averaged values of penetration rate, rotation speed and MWD (measurements-while-drilling) values of torque and weight-on-bit to obtain a real time measurement of tooth wear, drilling efficiency and the in situ shear strength of the rock being drilled.